Hollow composite structures, or pressure vessels, here referred to as “vessels”, such as pressurized gas tanks, have traditionally been made out of metal such as steel or aluminum. However, in recent years, the use of composite vessels has become more prevalent. Such vessels are manufactured by a variety of processes, which include but are not limited to filament winding, resin transfer molding and bladder-assisted molding.
Most composite material exhibit a relatively high permeability to many fluids. It is therefore usually necessary to provide a barrier liner within the pressure vessel in order to prevent excessive leakage. Certain polymer based liners offer good resistance to permeation, heat and chemical attack, making them suitable for high pressure media storage. It is known in particular to include a HDPE liner in filament-wound composite vessels.
Furthermore, high pressure vessels require monitoring to avoid overfilling and to detect leakage. This is usually achieved through pressure sensors and regulators at the vessel neck. Such external pressure gauges are relatively expensive and they are usually fitted to the vessel only during service. For the rest of the time, in particular during storage and transportation phases, the pressure in the tank cannot readily be known. In order to overcome this drawback, patent document WO 2011/104 295 discloses a pressure vessel comprising a liner exhibiting both barrier and piezoelectric properties. Piezoelectric materials have shown suitability as pressure sensors, as they produce a charge when subjected to an external force, allowing changes in pressure to be measured. Accordingly, the above prior art document teaches that by using the piezoelectric liner to monitor the pressure inside the pressure vessel, it is possible to dispense with the external pressure gauge. Patent document WO 2011/104 295 is incorporated by reference.
One difficulty with the above solution is to provide a liner that combines excellent barrier properties with an intense piezoelectric effect. It is therefore the main object of the present invention to provide such a liner.